In order to reduce NOx emissions from diesel and gasoline engines, it is known to use the “Miller process” to cool or reduce the combustion temperature. According to this process, a cooling effect is achieved by closing the intake valves very early. The subsequent expansion of the volume of gas in the combustion chamber lowers the temperature of the fresh gas mixture and the cylinder filling loss of the charged engine is compensated by an increased charging pressure generated by a turbocharger.
For transient engine conditions, in which the loaded engine must generate increased power/torque within a short time, shutting-off the Miller process is very helpful. This can be achieved by displacing the inlet cam profile by rotating the cam shaft relative to the crankshaft or by displacing the cam on the cam shaft or by modifying the coupling of the cam/valve. In all cases, a valve-opening overlap and thus evacuation of the cylinders is reduced by displacing the cam profile.
In EP 1 477 638 A1A, a device for variably controlling the opening and/or closing of inlet and/or exhaust valves of an internal combustion engine of the above-mentioned type is disclosed. This known device is adapted to delay the closing of inlet valves of an internal combustion engine, and includes a damping device integrated in a guide rod for guiding a valve actuation bridge during its up and down motion. Hence, the damping device is an integrated part of the valve actuation bridge. More particularly, in this known device, an annular recess is disposed between a guide rod of a piston and a cylinder sleeve. The annular recess is in fluid communication with an axial bore axially extending within the guide rod via a transverse bore. One end of a tap bore opens or discharges into the axial bore of the guide rod. The other end of the tap bore is in fluid communication with valve units via oil-supply lines. More particularly, the tap bore is connectable with a lubricating oil-supply port as a function of the valve position of the gas exchange valves either via a first oil-supply line controlled by a valve unit, which includes a passage and shutoff valve, or via a second oil-supply line controlled by a second valve unit, which includes a one-way valve and a throttle. Thus, controlling of the gas exchange valves as a function of the closed position and/or the opened position can be achieved by means of the valve units having the correspondingly-designed valves.
When the gas exchange valves are closed, lubricating oil contained in the annular recess can be supplied into a further valve unit via the axial bore and the tap bore, as well as via an oil-supply line. In addition, when the valve is closed, the lubricating oil can be supplied into the valve unit having the throttle so that the intake valves will assume a delayed position. In contrast, when the gas exchange valves are in a delayed position, the free or terminal end of the rocker arm that is opposite of the valve actuation bridge is pivoted about the rotational axis towards the rocker arm by means of a telescoping member, which is spring-biased and guided in the push-rod, without any play or clearance therebetween.
However, the device disclosed in EP 1 477 638 A1 requires construction space between the two inlet and/or exhaust valves and its associated springs. Furthermore, due to the integration of the damping device in the guide rod of the valve actuation bridge, the known device requires a guide rod.
U.S. Pat. No. 3,520,287 discloses an exhaust valve control for an engine braking system which also includes an arrangement having a guide rod slidably mounted on a valve actuation bridge. The valve actuation bridge and the guide rod together define a hydraulic chamber that expands when the valve bride advances to open the exhaust valves and contracts when the valve actuation bridge retracts to permit the two exhaust valves to be closed by the exhaust valve springs. Again, a damping device is integrated into the guide rod and is part of the valve actuation bridge. Hence, like the above arrangement, a construction space between the two valves is necessary and this known assembly requires a guide rod.
U.S. Pat. No. 6,905,155 discloses an apparatus for limiting the travel of a slave piston in a slave piston cylinder in a compression release engine retarder. The apparatus is connected to a hydraulic circuit and an internal passageway is defined in the slave piston head. The internal passageway comprises a vertical bore, a horizontal bore and an annular channel which together define a path for bleeding off the pressure at the top of the slave piston when the annular channel and an aperture in the slave piston cylinder are aligned. By bleeding off the hydraulic pressure at top of the slave piston, the motion of the slave piston is restricted to a desired stroke. The apparatus includes a locking adjustable foot on the slave piston stem which provides a means for adjusting the lash. Here, the known arrangement for actuating at least one engine valve requires a minimum space above the valve actuation bridge and the rocker arm.
US 2005/0121008 A1 discloses a method and apparatus for controlling a temperature in a combustion cylinder in an internal combustion engine. A rocker arm is located to move about a pivot. A push-rod provides a mechanical force against the rocker arm. An electro-hydraulic assist actuator may include a plunger assembly for providing a hydraulic force used to vary the open duration of an intake valve. In particular, the electro-hydraulic assist actuator may be used to hold the intake valve open for a period of time longer than a cam is designed to do. The plunger assembly may be located at the same side of the rocker arm as the push rod. In addition, the plunger assembly is designed to provide a mechanical force during a first rotating direction of the rocker arm. A reverse rotating direction of the rocker arm has no impact on the plunger assembly. Consequently, the known plunger assembly may be relatively slow and the reaction time could be relatively long.
US 2003/0221644 A1 shows a similar engine valve actuation system including a fluid actuator configured to selectively prevent an intake valve from moving in a first position.
Other arrangements are known from, e.g., DE 102 39 750 A1, US 2005/0121637, US 2004/0065285 A1, WO 2004/005677 A1, WO 87/07677.
The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior devices and methods for controlling valves and, more particularly, of apparatus for adjusting or delaying the closing of inlet valves of an internal combustion engine.